A Neural Builder for Spatial Subdivision Hierarchies

This repository contains the source code of the paper: A Neural Builder for Spatial Subdivision Hierarchies, published in The Visual Computer and presented at the Computer Graphics International 2023 conference.

The code, written in Python, showcases how to train and test the network with both a default and your own model, in order to infer a fixed-level tree structure. The resulting fixed-depth tree can then be further expanded, in parallel, into either a full k-d tree or transformed into a bounding volume hierarchy, with any known conventional tree builder. For more details on the last part, please see the paper.

Table of Contents

• Prerequisites
• Downloading the Dataset
• Training the Model
• Testing the Model
• Building your Own Dataset
• How to Cite
• Acknowledgments
• Contact Us

Prerequisites

The code has been tested on Python 3.9 and requires the following packages to be present in your environment:

trimesh
numpy==1.24.3
pandas==1.4.3
tensorflow==2.10.1
matplotlib==3.5.3
seaborn==0.11.2

Downloading the Dataset

The dataset used both in the paper and this code is available here (1GB - 2.6GB extracted). Download and extract it at the root folder of the project.

Details:

• The dataset directory is at datasets/custom_scenes
• The scene folders contains every individual scene in a separate folder, in polygon and point cloud format
• The index to the training or test data is located in the train_fragments_2048 and test_fragments_2048 csv files, respectively, where 2048 is the point cloud size (see next section)

Training the Model

The code is configured to train and test an example model. To initiate training, simply run:

python model_train.py

The file global_config.py contains a set of hyperparameters that are used to tune the network. The most prevalent are:

• pc_size: the point cloud size (assumes point clouds in dataset to be of the same size, e.g. 2048)
• lvls: the maximum training depth
• epochs: the number of epochs to train
• capacity: the number of filters for the encoders
• batch_size: the batch size to train with

Some extra information:

• The set of hyperparameters dictates the model name, e.g. sah_kdtree_3lvl_2048pc_128capacity_model_name. Here, model_name is a user defined variable set in the class constructor (see model_train.py)
• You may resume training using the model's .continue_training() functionality. Please note that this function loads the last recorded model parameters and optimizer's state from metadata directory and appends the statistics cached in the plots/your_model_name existing directory

Relevant output during the training process is cached in the plots/your_model_name directory. This folder contains (for each trained model):

• Training-specific diagrams
• A model checkpoint containing the parameters and optimizer's state, of the best in terms of tree cost model, cached in plots/your_model_name/your_model_name_c/ directory
• The metadata folder contains the model from the last recorded epoch

Testing the Model

To test the trained network, simply run:

python model_test.py

As discussed in the paper, the steps performed in this operation are:

• A scene is loaded from a predefined folder
• The primitive population is sampled
• An instance of treeNet_model.neural_kdtree is created, using the same name and global_config parameters that it was trained with
• The model parameters are loaded from the metadata folder for the associate model. To load the best recorded model one has to pull the file parameters located in plots/your_model_name/your_model_name_c/ directory
• The tree structure (planes/offsets) is computed with greedy and recursive inference functions
• The output is stored in binary files in the plots/predict hierarchy folder with the scene's corresponding name. The internal node layout is cached in a level-order fashion

This data can be used as a fixed-depth tree and then expanded into a k-d tree or a BVH using known conventional tree builders. See details in the paper.

Building your Own Dataset

An example model is used by default, which loads all scenes at the dataset folder. To use your own dataset, you need to add a new folder with your own scenes at the datasets folder, where each scene is also stored at its own folder, similar to datasets/custom_scenes.

Then, you need to follow the helper functions in the dataset_builder.py script. For example:

• The build_pc function contains the code used to construct the point clouds from the polygon soup
• The build_vh_dataset and build_sah_dataset functions contains the code for training, testing and validating SAH and VH, respectively. This essentially creates:
  • A train folder containing the pointclouds along with the associated .csv to index them
  • A test folder containing folders for each scene with point clouds sampled from the whole population, along with an associated .csv to index these point clouds during training for validation

Extra notes:

• Further details on the construction and extraction process of these point clouds are in the paper
• Manually adding/removing/excluding point clouds from these folders during training requires to modify the associate .csv files

How to Cite

The license is MIT. If you use the contents of this repository for your work, please cite it as described below:

In our work, we have used the source code~\cite{Evangelou_2023_CGI_2023}, available at ' https://github.com/cgaueb/nss'.

@article{Evangelou_2023_CGI_2023,
	title    = "A neural builder for spatial subdivision hierarchies",
    author   = "Evangelou, Iordanis and Papaioannou, Georgios and Vardis, Konstantinos and Gkaravelis, Anastasios",
	journal  = "The Visual Computer",
	volume   =  39,
	number   =  8,
	pages    = "3797--3809",
	month    =  aug,
	year     =  2023,
    DOI      = {10.1007/s00371-023-02975-y}
}

Acknowledgments

This research was funded by the Hellenic Foundation for Research and Innovation (H.F.R.I.) under the “3rd Call for H.F.R.I. Research Projects to support Post-Doctoral Researchers” (Project No: 7310, LOTUS).

Credits for the included scenes (per-scene credits are in Figure 2 of the paper):

• Rendering resources by Benedikt Bitterli
• Scenes for pbrt-v3 by Matt Pharr, Jakob Wenzel and Greh Humphreys
• Amazon Lumberyard Bistro, Open Research Content Archive (ORCA) by Amazon Lumberyard
• Computer Graphics Archive by Morgan McGuire

Contact Us

For any assistance, please contact at iordanise@aueb.gr (1st author) or kvardis@aueb.gr. Thank you!